Split alu frame: Welding fix possible?

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esuhl
Posts: 155
Joined: 22 Mar 2017, 3:20am

Split alu frame: Welding fix possible?

Post by esuhl »

The aluminium frame on my bike has split at the top of the seat-tube. Is there any chance it could be repaired? Would it be expensive...? :?

I've searched for companies, but only found one: All Metal Welding Services in Hammersmith. Has anyone else used them...?

Cheers :-)

PHOTO (crack highlighted in red oval):
https://www.dropbox.com/s/z63gdjvnchbh3 ... ght%29.jpg
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SimonCelsa
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Joined: 6 Apr 2011, 10:19pm

Re: Split alu frame: Welding fix possible?

Post by SimonCelsa »

My alloy framed tandem weld repair is still holding OK:

viewtopic.php?f=5&t=137608&hilit=tandem+scrap

However, it's only covered around 750 miles since the repair and I ride it a lot more cautiously than before!

I would say the repair you are looking at is more problematic due to seat post insertion and associated clamping forces (although I am no expert, merely an observation)
PT1029
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Joined: 16 Apr 2012, 9:20pm

Re: Split alu frame: Welding fix possible?

Post by PT1029 »

It would be good to see a wider view photo, ie, how far above the top tube does the seat tube extend, and how much seat post sits in the frame/what lenght sticks out the top.
It would be interesting (to some at least) to see if the crack is due to a metal/welding fault (which could be the case, the crack does seem suspiciously in line with the top tube), or possibly a long seat post leverage issue (is the crack near where the bottom of the seat post used to be?, are you a heavy rider?).
If you got it welded, I'd try to get a longer seat post that extends below the weld, just to give everything a better chance of not re cracking.
If the new weld extends to the seat tube interior, you might need to get it reamed out (or take pot luck with a rounded file).

In the past I have had an aluminium cargo bike welded twice (Oxford area, the better one was near Witney). One seemed to do more work with welding tubes and did a better looking job than the one who seemed to do more thick plate/beam welding.
slowster
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Re: Split alu frame: Welding fix possible?

Post by slowster »

It might help if you told us what the bike/frame is. Obviously if it is a relatively cheap frame, it will more likely that the cost of a good professional repair will make it not cost effective compared with a replacement frame. Additionally I think that the grade of aluminium alloy can be a factor in the viability of repair.
jb
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Joined: 6 Jan 2007, 12:17pm
Location: Clitheroe

Re: Split alu frame: Welding fix possible?

Post by jb »

A motorcycle frame repair specialist did a repair to an aluminium 'Orange' frame for me once. There might be one near you.
Cheers
J Bro
esuhl
Posts: 155
Joined: 22 Mar 2017, 3:20am

Re: Split alu frame: Welding fix possible?

Post by esuhl »

SimonCelsa wrote: 3 Aug 2021, 5:55amI would say the repair you are looking at is more problematic due to seat post insertion and associated clamping forces (although I am no expert, merely an observation)
Yeah -- I wondered if a fix might require welding the seat post in place. Having read your tandem thread (and others), I'm a bit worried about the mentions of aluminium's "finite fatige life"... I assumed an alu frame would last "forever". :-/
slowster wrote: 3 Aug 2021, 8:35amIt might help if you told us what the bike/frame is. Obviously if it is a relatively cheap frame, it will more likely that the cost of a good professional repair will make it not cost effective compared with a replacement frame. Additionally I think that the grade of aluminium alloy can be a factor in the viability of repair.
Apparently the frame is "6061 aluminium". It's a 2010 edition B'Twin Rockrider 8.1 that was £500 new. But I recently spent a fortune on upgrades. And I'm really confused about how I'd find a frame that would be compatible with them. I live in a village and don't drive, so finding secondhand frames/bikes isn't easy.

Sigh. I really don't know what to do. :-(
PT1029 wrote: 3 Aug 2021, 8:18amIt would be good to see a wider view photo, ie, how far above the top tube does the seat tube extend, and how much seat post sits in the frame/what lenght sticks out the top.
Sure. Here's a wider view:
https://www.dropbox.com/s/8b1thxcrle4vc ... 20view.jpg

And this shows the seatpost length. If you zoom in there's a scratch almost exactly in line with my thumb (I'm holding it 4 or 5 mm higher than it should be):

https://www.dropbox.com/s/kxt4xyfhb20j7 ... 20post.jpg
PT1029 wrote: 3 Aug 2021, 8:18amIt would be interesting (to some at least) to see if the crack is due to a metal/welding fault (which could be the case, the crack does seem suspiciously in line with the top tube), or possibly a long seat post leverage issue (is the crack near where the bottom of the seat post used to be?, are you a heavy rider?).
Yes -- the "messy blob" of metal on top of the top-tube has split away from the top-tube itself. The split extends round 70% of the circumference on both sides of the bike, with just the rear 30% attached. Worse than I realised... :-/

I'm not a heavy rider in weight (70kg) or in riding style... but I often carry heavy loads in panniers on a bike not designed to have a pannier rack... and yank the bike around by lifting it from the saddle. Oops.
DevonDamo
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Re: Split alu frame: Welding fix possible?

Post by DevonDamo »

[Deleted - duplicate post.]
Last edited by DevonDamo on 4 Aug 2021, 5:25pm, edited 1 time in total.
DevonDamo
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Re: Split alu frame: Welding fix possible?

Post by DevonDamo »

esuhl wrote: 4 Aug 2021, 4:26pmAnd this shows the seatpost length. If you zoom in there's a scratch almost exactly in line with my thumb (I'm holding it 4 or 5 mm higher than it should be):
Not the question you're asking, but From that photo, I'd say 'PT1029' has nailed it with his second hypothesis above: it's a seatpost leverage issue. Yes, you're inserting it well below the minimum insert line, but that frame has a long section of seat tube protruding vertically from the junction with the top-tube which, in terms of structural strength, does very little to prevent any leverage on the seat tube doing damage. This means that if you were to line up the minimum insertion line with the top of the seat tube, the bottom of the seatpost would be level with the midpoint of the top tube. You really want the seat tube extending at least a couple of inches below the top tube to avoid putting too much leverage on the frame at that point.

I've broken a frame on a folding bike for the same reason. I was able to fix it by wrapping the broken section in fibreglass tape and installing a telescopic seat post (to increase the amount the seat tube extends into the frame) but that's clearly a bodge which most people wouldn't accept. I think the fact that (1) the crack is in an awkward position, running along an existing frame weld and (2) the bike is too small for you anyway, a second-hand frame would be a better solution than a frame repair.

You had some sensible suggestions on what sort of frame or bike to go for in your previous thread about what to do. Personally, my recommendation would be to just buy a complete, quality, second-hand hardtail, around 7 or 8 years old that's big enough for you. Your £500 budget should get you something of that vintage with components at least as good as the ones you've bought - e.g. £275 got me a 2014 Cube Race Ltd 29er, which came with Rockshox Reba 100 SoloAir forks - a step up from the Recons. You might need to spend a bit of money doing it up, but you could fund that by selling the various components you've got on and off the bike.
Jamesh
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Joined: 2 Jan 2017, 5:56pm

Re: Split alu frame: Welding fix possible?

Post by Jamesh »

Could you pick up a frame from eBay or gumtree and have it delivered?

Cheers James
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SimonCelsa
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Joined: 6 Apr 2011, 10:19pm

Re: Split alu frame: Welding fix possible?

Post by SimonCelsa »

If you're really sentimentally attached to the frame then you could possibly fabricate a super-long wedge style seatpost.

I did a similar fix for a friend although it was only a short one. See here: viewtopic.php?f=5&t=123718&hilit=wedge+seatpost

Just an idea, maybe a daft one!!
mattsccm
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Joined: 28 Nov 2009, 9:44pm

Re: Split alu frame: Welding fix possible?

Post by mattsccm »

Perfectly fixable although your welder may need to be friendly if it doesn't stick well. My alloy welding jobs have been done by my brother for beer. Commercially may be tricky. Snag will be how round the tubing is after it is done. Shove a steel seat post, or better still and exact size bit of solid ba down it whilst it is welded. Still might need reaming out or maybe a round file.
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